The present invention relates to power detection systems and methods, and more specifically to detection and monitoring of power supply voltage and voltage reference circuitry.
The function of voltage reference circuitry in an electronic circuit device or system is to provide a constant reference voltage for other part of the circuit in the system. The constant reference voltage may be used by a Power On Reset (POR) circuit in order to keep the system in a reset state during system power-up, thus preventing an unknown initial state in the system.
Conventional POR circuitry usually consists of a simple resistor-capacitor (RC) delay circuitry that generates a reset signal for a predetermined amount of time during system power up, thereby keeping system in reset state for the predetermined period of time. However, use of such RC delay POR circuitry requires the assumption that the power supply voltage will have reached its stable-state value after the predetermined amount of time has passed. Additionally, RC delay POR circuitry is not reliable because it does not directly detect the power supply voltage level. Furthermore, the delay provided by the RC delay POR circuitry has large variability over variations in process, temperature, and power supply voltage (PVT), and accordingly provides a smaller operating margin, especially for low power systems. Moreover, RC delay POR circuitry lacks power supply dip or brownout detection, which is important for robust system operation.
Field programmable gate array (FPGA) devices have in the past employed POR circuitry that compares the voltage levels provided by all of power supplies against a bandgap reference voltage level output by an on-chip bandgap reference circuitry. Because bandgap reference circuitry provides an accurate and stable bandgap reference voltage level during steady-state operation, the POR circuitry may compare voltage levels of the power supplies to accurate and stable thresholds, thereby generating reliable and accurate system reset signal(s). However such comparison POR schemes only work for the detection of other power supplies, and not for the power supply of the bandgap reference circuit itself because during the power-up or brown-out of this power supply, the bandgap circuit is not stable and the comparison POR circuitry may not be referencing a correct reference level.